This invention relates to a sputtering target capable of forming easily and uniformly, a film resistor having high specific resistance, excellent heat resistance, and anti-corrosion property, a film resistor using such a sputtering target and a thermal printer head using such a film resistor.
A thermographic type recording apparatus using a thermal printer head has been used as a recording apparatus in facsimiles machines, copiers and ticket venders with the advantages low noise and less maintenance. In such thermal printer heads, tantalum nitride has been used as a stable material for a film resistor to fuse a printing medium. The Ta-N type film is produced by reactive sputtering a Ta target in a nitrogen environment and although the specific resistance becomes larger as the nitrogen content is increased, Ta.sub.2 N has been generally used as a heat generating film resistor because of its reliability and stability.
However, Ta.sub.2 N itself has specific resistance of approximately 200 .mu..OMEGA.cm and even if the thickness of the film is made very thin to increase the specific resistance, there is a limit in the maximum value. For example, to obtain the resistance of 200 .OMEGA. using Ta.sub.2 N, it is necessary to form a strip shape with 2:1 in the ratio of length and width and thickness of approximately 20 nm. When making such thin films, the control of thickness is very difficult and the reproducibility and uniformity of the film decreases, and consequently the film is easy to damage by increasing the power density.
To improve the defects aforementioned, an idea of forming a film resistor to be a meander type increasing the effective length per unit area thereby increasing the resistance was proposed. However, as the resolution of thermal printer head increase, more high technology for patterning is required and it results in the lowering of the yield. Furthermore, in the manufacturing process, a reactive sputtering method is used wherein the amount of gas introduced into the vacuum reactor is very small and controlling the introduction of such amounts requires exact technology.
On the other hand, Japanese Patent Application Laid-open No. SHO 52(1977)-109947 discloses that high specific resistance film is obtained by using a target where a hollow quartz disc is filled with a heat generating resistor such as TiC. Though the film has excellent oxidation resistance at high temperatures, the control of the composition of the film is difficult and the fluctuation of sheet resistance in the substrate is large.
The application of a thin thermet film to obtain high specific resistance is proposed. As a thermet film, a Ta-SiO.sub.2 resistor film and the like is used and it has been made by, e.g., a multi source sputtering method using, for example, both a Ta target and a SiO.sub.2 target. However, since the sputtering angles of Ta and Si differ greatly, the compositions of the Ta-SiO.sub.2 resistor film and the target deviate from each other due to a slight change of sputtering conditions and the control of the composition of the film is difficult. Because of the aforementioned reasons the composition of the film tends not to be uniform and it results in undesirable large fluctuation of the sheet resistance and less reproducibility.
An object of the present invention is, considering the points mentioned above, to provide a sputtering target which is capable of forming a high specific resistant film with an uniform composition, which is the almost same as that from that of the target. Another object of the present invention is to provide a film resistor with high specific resistance, excellent heat resistance and anti-corrosion characteristics while controlling the fluctuation of the sheet resistance in the film. A further other object is to provide a thermal printer head capable of high speed operation improving the resolution of printed images, using the aforementioned film resistor.